Local loop by traditional definition is that portion of a network that connects a subscriber's home to a central office switch. This is, however, an expansive definition that does not hold true as the network extends into the local loop by means of Digital Loop Carrier and Digital Cross Connects. For the purposes of this invention, local loop is considered as the connection from the subscriber's premises to the connecting point in the network, whatever the nature of that connection may be.
Until recently the local loop was mostly based on copper plant supplemented by microwave radio links for remote areas or difficult terrain. Over the last decade fiber optics have made significant inroads into the local loop (also referred to as "access" network) reaching closer to subscriber homes and buildings. Sonet based access networks bring fiber to the curb. These fiber based solutions can provide very high bandwidth services, reliably and cost-effectively, in urban/metropolitan areas with significant numbers of business customers. In fact, most access providers in the U.S. have used such fiber based plant to provide access services to U.S. business customers.
The copper and fiber based solutions, while economical in many situations, still suffer from a number of drawbacks.
For example, in an area without an existing network infrastructure, it is very time consuming and expensive to build a new network. The expense is primarily in the labor, rights acquisition (for right of way or easement), and in electronics (for fiber based access). Overall the process is very slow due to extensive effort involved in acquiring right of way and in performing the required construction, aerial and/or underground. Also, in locations with extensive but congested existing infrastructure, it is often very expensive to add capacity due to already full ducts and cables, and sometimes impossible to add capacity without resorting to upgrading the entire system. In addition, wireline solutions tend to have costs that are distance sensitive, hence they are inherently unsuitable for sparse/scattered demand. Wireline networks are also not amenable to redeployment, which results in stranded assets when demand (consumer) moves. Wireline networks also cannot be rapidly deployed in emergency situations.
The term "fixed wireless loop", or FWL, connotes a fixed wireless based local access. However, it is often mixed with limited mobility solutions under the broader term "Radio Access". Irrespective of the type of radio technology, all fixed wireless or radio access systems use wireless means to provide network access to the subscriber. Broadly speaking, there are three main categories of fixed wireless solutions.
Fixed cellular systems are primarily based on existing analog cellular systems such as AMPS (in North America) or NMT (in Nordic countries).
Fixed cordless systems are primarily based on the European DECT standard using digital TDMA Time Division Duplex technology.
Bespoke systems are designed specifically for fixed wireless application. Conventional systems in this category are the analog microwave point to multi-point systems. More recently deployed systems operate at higher frequencies and employ digital technologies. These systems may be derived from similar cellular technologies, but are not based on any existing agreed upon standards.
Of the three main categories of fixed wireless systems there is no one solution that is clearly superior to others. If the primary need for a system operator is to provide voice oriented service wherein voice quality is not a limiting factor, then often a fixed cellular system is adequate, and even desirable because of its relatively low equipment cost. For very high density urban situations, a DECT solution may be desirable due to its high load carrying capacity and its pico-cellular architecture. Microwave solutions are best for sparse populations. Bespoke systems function well over a wide range of situations and have the best overall quality and desirable features, however they are likely to be more expensive, at least in the near future.
Most residential consumers in developing economies are mainly interested in adequate voice service. However, most business customers require data and fax service in addition to voice. With the growing popularity of home computers and Internet access, a need is arising to provide residential consumers with high speed data services at home. As such, the general trend is in the direction that all customers, both residential and business, will demand high quality voice and data services.
A problem that arises in conventional Code Division Multiple Access communications systems relates to system capacity constraints imposed by the finite number of available pseudonoise (pn) spreading codes. This problem is compounded when two pn codes are used in one channel for spreading (and despreading) the Inphase (I) and the Quadrature (Q) symbol pairs.
Another problem in conventional communication systems relates to the transmission of control messages. Typically, control messages are put on a queue for earliest transmission, and frame structures are typically designed to transmit all control messages for a particular frame in a single block either at the beginning or end of the frame. However, this approach adds a delay in order to transmit all control for a particular frame in a single block either at the beginning or end of the frame. For example, if a one byte message is at the top of the queue when a new frame ends, this message cannot be transmitted for an entire frame until the next block is ready to be sent. In this case, the delay would be an entire frame.